This invention relates to new compositions and to the preparation of foamed polyester resins therefrom. In particular, it relates to storage stable dispersions of symmetrical or asymmetrical aromatic diacyl peroxides and their use in the curing and foaming of unsaturated polyester resins.
The use of aromatic diacyl peroxides as polymerization initiators is particularly important in the curing and foaming of unsaturated polyester resins. This technique is useful in the preparation of shaped objects.
The preparation of foamed polymeric products can be accomplished by the introduction of compounds which liberate carbon dioxide as a blowing agent into the polyester resin. U.S. Pat. No. 3,224,983 discloses the use of organic carbonates, such as sodium carbonate and sodium bicarbonate for this purpose.
Other patents showing the use of carbonates and bicarbonates to produce foamed polyester products include U.S. Pat. No. 4,016,112 which uses phosphoric and phosphorus acid esters to react with such carbonates and bicarbonates at temperatures as low as 20.degree. C.; U.S. Pat. Nos. 3,479,303 and 4,028,289 which describe stabilized polyester resin products foamed by the use of bicarbonate of soda; and U.S. Pat. No. 4,347,331 uses the reaction product of aqueous aluminum hydroxide chloride solution and inorganic carbonate or bicarbonate compounds.
The use of aromatic diacyl peroxide as a polymerization initiator is also known and reported in the literature. Previously referred to U.S. Pat. No. 4,016,112 discloses the use of polymerization initiators in the production of cured foamed structures using the carbonic acid gas generated by the reaction of metal carbonates or bicarbonates with acid substances containing various peroxides including benzoyl peroxide, di-tertiary butylperoxide, etc. The use of peroxide catalysts for the preparation of foamed polyester resins is also disclosed in U.S. Pat. No. 4,028,289.
U.S. Pat. No. 4,692,427 discloses aqueous dispersions of symmetrical and asymmetrical aromatic diacylperoxides. The use of these dispersions in making a foamed polyester resin is claimed in our U.S. Pat. No. 4,711,909.
Just as aqueous dispersions of organic peroxides and their use as polymerization initiators are well known, it is also appreciated that the use of these aqueous dispersions can have certain drawbacks in many systems which are sensitive to the presence of large quantities of water. For example, U.S. Pat. No. 3,507,800 which is directed to providing aqueous dispersions of organic peroxides, acknowledges the need to reduce the percentage of water in the dispersion for certain applications (see column 2, lines 16-19).
On the other hand, reducing the percentage of water in aqueous dispersions leads to an increase in the viscosity of the dispersion, affecting the pumpability of the dispersion.
Accordingly, it is an object of the present invention to reduce the water content of dispersions of aromatic diacyl peroxides.
It is another object of the present invention to devise dispersions useful for the curing and foaming of unsaturated polyester resins.
Still another object of the present invention is the preparation of aqueous dispersions of organic diacyl peroxides having reduced viscosities.
Also an object of the present invention is a method for foaming and curing unsaturated polyester resins by the use of a stable composition comprising an organic diacyl peroxide.
Also an object of the present invention is a method for foaming and curing unsaturated polyester resins by an aqueous dispersion of an organic diacyl peroxide having a reduced water content.
Other objects of the present invention will become readily apparent from the ensuing description.